$ F = \left[\begin{array}{rr}1 & -2 \\ 0 & 4 \\ 0 & 2\end{array}\right]$ What are the dimensions of matrix $ F$ ?
Explanation: The first dimension is the number of rows in the matrix. How many rows does $ F$ have? The second dimension is the number of columns in the matrix. How many columns does $ F$ have? So, $ F$ is a 3 $\times$ 2 matrix.